A wide variety of roller cone and rotary cone drill bits have previously been used to form wellbores or boreholes in subterranean formations. Roller cone drill bits generally include at least one support arm and often three support arms. A cone assembly may be rotatably mounted on a spindle or journal extending inwardly from an interior surface each support arm. Small gaps are generally provided between adjacent portions of each support arm and associate cone assembly to allow rotation of the cone assembly relative to the respective support arm and spindle while drilling a wellbore.
Protection of bearings and related supporting structures which allow rotation of a cone assembly relative to an associated support arm and spindle may lengthen the life of an associated roller cone drill bit. Once downhole debris is allowed to infiltrate between bearing surfaces of a cone assembly and associated spindle, failure of the drill bit will generally follow shortly thereafter. Various mechanisms and techniques have been used to prevent debris from contacting such bearing surfaces.
A typical approach is to install a fluid seal in a gap formed between adjacent portions of each cone assembly and associated spindle. Such fluid seals maintain lubrication in bearings and associated supporting structures and prevent intrusion of shale, formation cuttings and other types of downhole debris. Once the fluid seal fails, downhole debris may quickly contaminate bearing surfaces via the gap. Thus, it is important that fluid seals also be protected against damage caused by downhole debris.
Various approaches have previously been used to protect fluid seals in roller cone drill bits from downhole debris. One approach is to install hardfacing and/or wear buttons on opposite sides of gaps formed between each cone assembly and associated support arm on exterior portions of the drill bit. Hardfacing and wear buttons generally slow erosion of metal adjacent to such gaps to prolong downhole drilling time before an associated fluid seal may be exposed to downhole debris. Another approach is to form tortuous fluid flow paths proximate each gap leading to an associated fluid seal. Tortuous fluid flow paths allow rotation of a cone assembly relative to an associated spindle but are often difficult for downhole debris to follow.
Various types of debris diverter plugs, sometimes referred to as “shale burn compacts” or “shale burn plugs”, have been installed on interior surfaces of support arms proximate portions of an associated cone assembly. Such diverter plugs may block or direct fluids containing downhole debris away from an associated fluid seal. Also, debris diverter grooves, sometimes referred to as “shale diverter grooves”, have been formed in interior surfaces of support arms adjacent to an associated cutter cone assembly. Such diverter grooves may direct fluids containing downhole debris away from an associated fluid seal.